. >>> i'm liz crenshaw. hate dropped cell phone calls? find out which wireless carrier scored best ad which scored worst in our region. >>> which cell phone carrier has the best service in our area? >> is a 3,000 mile oil change rule really a myth? liz crenshaw is here with details on these stories. >> we begin with used car sales, the recession has csed used car prices to sore. with new car sales down, there are fewe late model trade-ins and that affects supply and demand. dealers are keeping older vehicles on their lots, rather than sending them to auction. when drivers keep cars longer rather than trading them in, dealers must pay top dollar for used car inventory. speaking of keeping your used car running smthly, how far should you drive before changing the oil in your car? break that habit of every 3,000 miles. it's a myth and ss because of technological advances, an average car's interest val is aroundp 7,800 miles now. the porsche can go 20,000 miles before an oil change. service centers and deers use the 3,000 mile change as a mar